U.S. patent number 4,640,573 [Application Number 06/460,804] was granted by the patent office on 1987-02-03 for lens-on-disc type optical scanning apparatus.
This patent grant is currently assigned to Hitachi Koki Co., Ltd., Hitachi, Ltd.. Invention is credited to Keiji Kataoka, Susumu Saito.
United States Patent |
4,640,573 |
Kataoka , et al. |
February 3, 1987 |
Lens-on-disc type optical scanning apparatus
Abstract
A lens-on-disc type optical scanner comprises a plurality of
lenses of predetermined surface profile arranged on a disc along
the circumferential direction of the disc. The disc is rotated so
that a laser beam from a laser beam source passes sequentially
through the lenses for optical scanning.
Inventors: |
Kataoka; Keiji (Kawagoe,
JP), Saito; Susumu (Hachioji, JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
Hitachi Koki Co., Ltd. (Tokyo, JP)
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Family
ID: |
12222598 |
Appl.
No.: |
06/460,804 |
Filed: |
January 25, 1983 |
Foreign Application Priority Data
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Feb 24, 1982 [JP] |
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57-27491 |
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Current U.S.
Class: |
359/210.1 |
Current CPC
Class: |
G02B
26/10 (20130101); G02B 3/00 (20130101) |
Current International
Class: |
G02B
26/10 (20060101); G02B 3/00 (20060101); G02B
026/10 () |
Field of
Search: |
;350/6.1,6.3,6.8,254,452 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0067721 |
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May 1980 |
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JP |
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55-79409 |
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Jun 1980 |
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JP |
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Primary Examiner: Corbin; John K.
Assistant Examiner: Gass; Rebecca D.
Attorney, Agent or Firm: Antonelli, Terry & Wands
Claims
What is claimed is:
1. A lens-on-disc type optical scanner comprising a first support
in the form of a disc, a plurality of lenses arranged on said first
disc along the circumferential direction of said disc and having a
first predetermined surface profile, a second support in the form
of a disc, and a plurality of lenses arranged on said second disc
along the circumferential direction of said disc and having a
second predetermined surface profile different from said first
predetermined surface profile, said first and second discs being
bonded together at their circumferential edges, wherein a scanning
plane located at a predetermined position is scanned by a laser
beam passing through said lenses sequentially by rotating said
first and second discs.
2. A lens-on-disc type optical scanning apparatus according to
claim 1, wherein said plurality of lenses are disposed on a circle
having a center which is the same as the rotation axis of each said
disc.
3. A lens-on-disc type optical scanning apparatus according to
claim 1, wherein each said disc and said lenses arranged on the
associated disc are made of resin and made in a body.
4. A lens-on-disc type optical scanning apparatus according to
claim 1, wherein said first surface profile is convex and said
second surface profile is concave.
5. A lens-on-disc type optical scanning apparatus according to
claim 1, wherein said first and second discs are arranged so that
said first surface profile is disposed opposite said second surface
profile.
6. A lens-on-disc type optical scanning apparatus according to
claim 5, wherein said first surface profile is convex and said
second surface profile is concave.
7. A lens-on-disc type optical scanning apparatus accoridng to
claim 5, wherein each said disc and said lenses arranged on the
associated disc are made of resin and made in a body.
Description
This invention relates to an optical scanning apparatus using a
laser beam for scanning, and more particularly to an optical
scanning apparatus employing an optical scanner having lenses
arranged on a disc (which scanner will be referred to hereinafter
as a lens-on-disc type optical scanner.
The prior art and the present invention will be described with
reference to the accompanying drawings, in which:
FIG. 1 shows the structure of a prior art optical scanning
apparatus employing a rotary polyhedral mirror as its optical
scanner;
FIGS. 2 and 3 are diagrammatic views illustrating the basic
principle of the lens-on-disc type optical scanner of the present
invention;
FIGS. 4 and 5 are characteristic curve diagrams showing the results
of calculation of the amount of deviation of the scanning line in
the arrangement shown in FIG. 2;
FIG. 6 is a perspective view of an embodiment of the lens-on-disc
type optical scanner according to the present invention;
FIG. 7 is a sectional view taken along the line X--X' in FIG.
6;
FIGS. 8 and 9 are sectional views of other embodiments of the
present invention;
FIGS. 10 and 11 are diagrammatic views of optical systems in each
of which the lens-on-disc type optical scanner of the present
invention is incorporated; and
FIG. 12 is a sectional view of another embodiment of the present
invention.
In an optical scanning apparatus such as that used in a laser
printer or a laser display, a rotary polyhedral mirror has been
employed as its optical scanner. FIG. 1 shows an optical system in
which a rotary polyhedral mirror is incorporated for scanning with
a laser beam. Referring to FIG. 1, the rotary polyhedral mirror 1
is rotated in a direction as shown by the arrow R1, and a laser
beam 4 is reflected by the mirror 1 for scanning on a display
screen 3. A lens 2 focuses the laser beam 4 into a minute beam spot
on the screen 3. A motor 5 causes the rotation of the rotary
polyhedral mirror 1 in the direction of the arrow R1.
In such an arrangement, each reflecting surface 1--1 of the rotary
polyhedral mirror 1 acts to produce a scanning line running in the
x-direction on the display screen 3. For scanning in the
y-direction on the screen 3, the screen 3 is moved at a
predetermined constant speed in a direction as shown by the arrow
7, so that the entire area of the screen 3 can be scanned with the
scanning line. The screen 3 may be a sheet of paper with or without
a coating of a photosensitive material or may be a display surface
having a phosphor coating. A beam modulator 6 modulates the
intensity of the laser beam 4 so that laser recording or display
with any desired beam intensity distribution on the screen 3 can be
provided.
However, the rotary polyhedral mirror 1 may not always be
manufactured to meet the severe dimensional requirement, and there
may be the so-called tilt of the mirror facet in the case of which
the lines normal to all of the reflecting surfaces of the rotary
polyhedral mirror 1 do not define the same angle with the axis of
rotation of the mirror 1. In such a case, irregularity occurs in
the scanning pitch for laser recording or display on the screen 3
in the y-direction shown in FIG. 1. Suppose, for example, that the
distance between the rotary polyhedral mirror 1 and the display
screen 3, which may be a photosensitive screen, is 600 mm, and the
allowable deviation of the scanning pitch on the photosensitive
screen 3 is 0.025 mm. Then, an angular accuracy of more than
is required for each of the reflecting surfaces of the rotary
polyhedral mirror 1. However, such an accuracy is almost the limit
of the manufacturing accuracy, and the rotary polyhedral mirror 1
will become quite expensive even if such an extremely high accuracy
could be achieved.
It is therefore a primary object of the present invention to
provide an optical scanner which is free from the prior art defect
pointed out above and is inexpensive.
The present invention which attains the above object provides a
lens-on-disc type optical scanner in which a plurality of lenses
are arranged on a support or disc along the circumference of the
disc which is rotated for scanning. The disc in the optical scanner
according to the present invention is made of a plastic material so
that it can be mass-produced at a low cost by a duplication
process. That is, a metal mold for forming the disc in the optical
scanner according to the present invention is previously prepared
so as to mass-produce the disc at a low cost by injection molding
or pressing.
FIG. 2 is a diagrammatic view illustrating the basic principle of
the present invention employing a plurality of lenses for optical
scanning.
Referring to FIG. 2, a laser beam 4 converging at a point C is
incident upon a lens 6 disposed on a support or disc (not shown).
The symbol A designates the center of the lens 6, and it is
supposed now that the lens 6 is displaced by a distance y.sub.o in
the y-direction from the optical axis of the incident laser beam 4.
Then, the laser beam 8 emerging from the lens 6 forms an image on a
screen 7 at a point y.sub.i which is approximately given by y.sub.i
=my.sub.o. In FIG. 2, the symbol f designates the focal distance of
the lens 6, and mf designates the distance between the lens 6 and
the screen 7. Therefore, the screen 7 can be optically scanned with
a scanning width which is m times as long as the distance of
translational movement of the lens 6.
FIG. 3 is a diagrammatic view illustrating how to calculate the
optical scanning characteristic when a laser beam 4 is incident
upon a lens 6 disposed on a disc 5 whose center is indicated by a
point B. It is supposed in FIG. 3 that the disc 5 rotates in a
direction as shown by the arrow, and the center A of the lens 6
makes an angle .theta. with the x-axis. It is also supposed in FIG.
3 that the laser beam 4 is incident upon the lens 6 at a point
(x.sub.1, 0) in the x- and y-coordinates, and the laser beam 4 has
an incidence angle .phi. with respect to the z-axis.
The center A of the lens 6 is spaced apart from the center B of the
disc 5 by a distance l. As in the case of FIG. 2, the lens 6 has a
focal distance f, and the distance between the lens 6 and a screen
7 is mf. Since the disc 5 rotates, a curved scanning line is
ordinarily produced on the screen 7. However, by suitably selecting
the incident point (x.sub.1, 0) and incidence angle .phi. of the
laser beam 4, it is possible to provide a rectilinear scanning line
on the screen 7. The reason why such a rectilinear scanning line
can be provided will be described with reference tc FIGS. 4 and
5.
FIGS. 4 and 5 are diagrams showing the relation between the
deviation .DELTA. of the scanning line and the scanning position
y.sub.i on the screen 7. Herein, the deviation .DELTA. of the
scanning line is defined as follows:
More precisely, FIG. 4 is a graph showing the results of
calculation of the relation between .DELTA. and y.sub.i using the
incidence point x.sub.1 of the laser beam 4 as a parameter, while
FIG. 5 is a graph showing the results of calculation of the above
relation using the incidence angle .DELTA. as a parameter, and it
will be seen that substantially rectilinear optical scanning can be
achieved. That is, FIG. 4 illustrates that the deviation .DELTA. is
zero irrespective of the value of the scanning position y.sub.1
when x.sub.1 =-3.32. Also, FIG. 5 illustrates that the deviation
.DELTA. at .phi.=1.6.degree. is -0.04 mm at the maximum when the
scanning position y.sub.i is within the range of 0.ltoreq.y.sub.i
<120 (mm), and the curve can be considered to be substantially
flat or rectilinear. The results of calculation shown in FIGS. 4
and 5 are based on f=50 mm, m=15, l=100 mm and .phi.=0.degree..
FIG. 6 shows the structure of an embodiment of the lens-on-disc
type optical scanner according to the present invention. The
lens-on-disc type optical scanner shown in FIG. 6 comprises a disc
8 made by injection molding or pressing a plastic material by use
of a metal mold, and a plurality of lenses 9 having a curved
surface profile and arranged along the circumferential direction of
the disc 8. The lenses 9 may be molded integrally with the disc 8
using plastic material. Suitable plastic materials include an
acrylic resin, a polycarbonate resin and a polystyrene resin. FIG.
7 is a sectional view taken along the line X--X' in FIG. 6 to
illustrate that lenses 9 are formed on the disc 8.
FIG. 8 is a sectional view of a structure in which a flat cover 10
of another plastic material covers the optical scanner shown in
FIG. 7 so as to protect the lens surface against damage. The flat
plastic cover 10 is bonded to the disc 8 of the lens-on-disc
optical scanner by an adhesive.
FIG. 9 is a sectional view showing the structure of another
embodiment comprising the combination of two lens-on-disc type
optical scanner elements 11 and 12. These optical scanner elements
11 and 12 include lenses of different surface profiles
respectively. That is, the optical scanner element 11 includes
lenses 14 having a convex surface profile, while the optical
scanner element 12 includes lenses 13 having a concave surface
profile. These optical scanner elements 11 and 12 are firmly bonded
together at their circumferential edges. According to the
lens-on-disc type optical scanner shown in FIG. 9, optical scanning
with corrected aberration of the optical system can be effected by
suitably selecting the refractive index of each of the discs and
the curved surface profile of the lenses on each of the discs.
FIG. 10 is a diagrammatic view of an optical system in which a
lens-on-disc type optical scanning apparatus 19 provided by
mounting a motor 17 on the optical scanner shown in FIG. 6 is
incorporated. A laser beam from a laser beam source 15 is converged
at a point C by a lens 16 and is then incident upon one of the
lenses arranged on the disc 8. The disc 8 is rotated in a direction
as shown by the arrow R.sub.2 by the motor 17 so that an optical
scanning line 18 is formed on a screen 7.
FIG. 11 shows an optical system in which cylindrical lenses 21, 22
and 23 are additionally inserted in the optical system shown in
FIG. 10. The arrangement shown in FIG. 11 further improves the
rectilinearity of the optical scanning line.
Although the foregoing description has referred to the arrangement
in which the lenses are concentrically arranged on the disc, it is
apparent that the lenses may be arranged in a helical pattern or
any suitable one of other patterns. Further Fresnel lenses 20
having a surface profile as shown in FIG. 12 may be arranged on a
disc 8 in a pattern as shown in FIG. 6.
* * * * *